1. Field of the Invention
The invention relates to a continuous dispersing apparatus in which stirring vanes in a vessel disperse pulverizing media.
2. Description of the Related Art
In producing printing ink, paint or the like, a mill base is used, which is formed by dispersing a powdered pigment in a varnish, a solvent or the like at a high concentration. In the dispersing process, a powdered pigment composed of secondary particles formed by agglutinating primary particles of the pigment is pulverized and dispersed in a varnish to produce fine particles not containing coarse particles. Such process is employed to improve the tinting strength of the printing ink and the paint.
To perform the above process, dispersing apparatuses such as a sand mill, a grain mill, a ball mill and the like are known. Dispersing apparatuses capable of preparing printing ink, etc., continuously are designed to continuously supply a mill base material from a material supply inlet that communicates with a vessel, a dispersing process is performed in the vessel, and thereafter the dispersed mill base is discharged continuously from a discharge outlet. However, since the supplied mill base material is not dispersed uniformly in the vessel, so-called "short-pass" occurs whereby mill base containing coarse pigment particles is discharged from the discharge outlet.
The problem of short pass can be prevented to a certain degree by increasing the rate of loading of pulverizing media. However, too high a rate of loading of the media induces choking, which results in an uneven distribution of the media on the discharge outlet side, thereby leading to unstable operation of the apparatus. To avoid this problem, the apparatus is operated at a rate of loading of the pulverizing media of about 75 to 80%.
In addition, U.S. Pat. No. 3,311,310 has been known as a conventional continuous dispersing apparatus as shown in FIG. 3. The conventional continuous dispersing apparatus includes a container 51, an outer mantle 52, a material feed sleeve 53, a stirring mechanism 54 having centrally rotating discs 60, a shaft 65 and circular discs 66, an intake socket 58, an discharge socket 59, counter rings 61, and bearings 62 and 63, in which the separation of the material being ground from the auxiliary grinding bodies is effected by cylindrical gaps formed between the centrally rotating discs 60 and counter rings 61. The stirring mechanism 54 is journalled in bearings 62 and 63 to permit changing the quantity or other characteristics of the auxiliary grinding bodies in an operative machine in zones x, y and z. However, the continuous dispersing apparatus has to be disassembled to overhaul. In case of the overhaul, if the stirring mechanism 54 including the centrally rotating discs 60 and the circular discs 66 are pulled out from the container 51, they may strike against the counter rings 61, whereby edge portion and/or other portions are chipped or broken by contacting each other. In addition, if the pulverizing media including hard materials made of steel, ceramic, stone, or the like runs against the top end portion of the counter rings 61 or the circular discs 66, it may chip or break their corners. Further, since the counter rings 61 can not release from the container 51 and the gaps between the counter rings 61 and the centrally rotating discs 60 are very narrow, it is difficult to overhaul to inspect or exchange the rings and the discs without striking each other and to adjust the gaps when the apparatus is re-assembled.